1. Technical Field of the Invention
The present invention relates to a lighting apparatus for lighting a light source and to a lighting fitting, and in particular to a lighting apparatus which is favorably used with LEDs (light emitting diodes) that serve as light sources and to a lighting fitting.
2. Related Art
Recently, semiconductor light sources, such as LEDs, have come into practical use as light sources of lighting fittings. Thus, lighting fittings using LEDs as light sources have come to be widely used. For example, as disclosed in JP-A-2007-035547, vehicle headlights are also suggested to use LEDs as light sources.
The life-span of LEDs is long compared to that of incandescent lamps of conventional art. LEDs are advantageous in that maximum quantity of light is available upon turning on the LEDs but are disadvantageous in that LEDs have a low tolerance for heat. For example, the temperature of a LED is raised by the heat generated with the emission of light from the LED. As a result, the element of the LED will be deteriorated to make the life-span of the LED shorter than the intrinsic life-span, or reduce the quantity of light emitted from the LED.
In this regard, the vehicle headlights disclosed in the above patent document JP-A-2007-035547 use a bracket as a heat sink, which is obtained by die-casting aluminum. Specifically, LEDs as light sources are mounted to such a bracket to discharge heat generated by the LEDs. With this configuration, temperature of the LEDs at the time of emitting light is suppressed from being raised.
A lighting fitting using LEDs as light sources is provided with a drive circuit used for turning on the LEDs. The drive circuit is separately provided being distanced from the LEDs. The drive circuit includes a temperature measurement section that measures temperature of the LEDs. The heat generated by each LED in emitting light is discharged from the LED to the air in the interior of the lighting fitting via a heat sink, such as a bracket. The heat transmitted to the air is dispersed in the entire interior of the lighting fitting by natural convection. The dispersed heat is measured by the temperature measurement section. In other words, the temperature measurement section measures temperature of the LEDs via the heat sink and the air in the interior of the lighting fitting.
The method set forth above for measuring temperature of LEDs via a heat sink and the air in the interior of a lighting fitting has suffered from a problem that the measurement is easily affected by external factors because the path used for temperature transmission is long, and thus it is difficult to accurately measure the temperature of the LEDs. In addition, the method has also suffered from a problem that, when the temperature of the LEDs changes, it takes time to measure the change of the temperature because the speed of transmission of the LEDs' temperature is slow.